The present invention relates to a remote visual inspection system for certain areas of vessels which are not accessible for inspection by personnel. It particularly relates to the visual inspection of a storage arrangement wherein there is a primary vessel for containing a fluid and an outer vessel, generally referred to as the guard vessel, which surrounds the primary vessel to prevent loss of fluid in the event of a rupture or leak in the primary vessel.
There are many reasons why a primary vessel containing a fluid would be contained within a guard vessel. For example, if the fluid is hazardous or dangerous to the environment, the guard vessel acts to catch and retain the fluid in the event of a leak in the primary vessel. In addition, when the primary vessel contains a fluid which is at an extreme temperature, for example, either a cryogenic fluid or a high-temperature fluid, such as would be found in a nuclear reactor, the space between the primary and guard vessels acts to provide insulation and minimize the loss of heat from the primary vessel to the environment.
A liquid metal-cooled nuclear reactor presents a particularly difficult problem since the space between the two vessels is at a relatively high temperature, generally 200.degree. C. or more. In addition, the space between the primary and guard vessels is maintained at a minimum. In the event of a rupture in the primary vessel, the fluid would drain into the annular space between the two vessels. This could create an extremely dangerous situation if the volume of the annular space allowed the fluid level in the primary vessel to reduce to a level to expose the reactor core. If the core is exposed, it would not receive sufficient cooling to prevent rupture and possibly melting of the core fuel assemblies, the result being fusion of the core. Thus, the space between the two vessels is maintained relatively small to prevent this possibility. The alternative is to maintain a sufficiently large inventory of coolant in the primary vessel to accommodate the volume of the annulus without exposing the reactor core, e.g., provide a larger and more expensive primary vessel.
To ensure continued safe operation of, for example, a nuclear reactor, periodic inspection at least of the primary vessel outer wall is required per the ASME Boiler Code, Section XI Division III. No reliable systems have been demonstrated for visually inspecting the narrow annulus that exists between a primary vessel and a guard vessel, particularly at the operating temperatures encountered in a nuclear reactor.
In addition to being able to inspect the interior of such an annulus, it also is necessary to know at all times precisely where the visual inspection device is located in order to compare, for example, current video tapes with video tapes made when the vessel was new. Further, in the case of nuclear reactors, the inspection system should not require any penetration in the guard vessel. The reason for this is that any such penetration could provide a source of leakage and defeat the purpose of the guard vessel.
Accordingly, it is an object of the present invention to provide a system which permits precise location of a remote visual inspection device for examining the annular space between a primary vessel and a guard vessel. It is another object of the invention to provide a remote visual inspection system which can withstand exposure to an extreme range of temperatures.